Instant messaging is form of real-time communication between two or more people based on typed text. The text is conveyed by data processing systems (e.g., computers, personal digital assistants, Blackberrys, etc.) over a network such as the Internet or an intranet.
Instant messaging offers real-time communication and allows easy collaboration, which might be considered more akin to genuine conversation than e-mail's store and forward/retrieve mechanism. In contrast to e-mail, the Instant Messaging parties know whether the peer is available via a Presence Service that is inherent in the Instant Messaging system. Most Instant Messaging systems allow the user to set an online status or away message so peers are notified when the user is available, busy, or away from the computer or do so automatically based on the user's activity level on their computer or activity within the Instant Messaging system itself. In most cases, the user is allowed to manually override the automated presence state. On the other hand, recipients of instant messages do not necessarily have to respond immediately to incoming messages. For this reason, users consider communication via instant messaging to be less intrusive than communication via telephone. However, some systems allow the sending of messages to people not currently logged on (offline messages), thus removing much of the difference between instant messaging and email.